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AV 123 are out of business with the owner in clink. So the possibilities for repair only exist for a crossover problem.
Most likely, they sourced the drivers from other manufacturers, and so one might be able to get new drivers anyway. One would want to pull a driver and inspect it for identification to find out what one can about this, as well as search online for information about them.
One way to test whether one has a speaker or crossover problem is to swap drivers from the bad speaker to the good one, and if the problem switches sides, then it is a driver problem, and if it does not switch sides, it is a crossover problem (assuming, of course, that one has eliminated all upstream components, such as amplifiers, from consideration).
It would be odd to damage all drivers in a speaker at once, but it is not impossible to do.